Growth Of Multi-walled Carbon Nanotubes Research Articles

Iron catalyzed growth of crystalline multi-walled carbon nanotubes from ambient carbon dioxide mediated by molten carbonates

Until now, research efforts focused on electrochemical conversion of carbon dioxide into stable carbon-based materials have been limited by poor understanding of catalytic effects occurring at surfaces. Here, we demonstrate the capability to simultaneously use atomic layer deposition (ALD), electrode composition control, and current density as a means to direct the formation of iron-based catalysts and grow highly crystalline multi-walled carbon nanotubes at high yields (99%) and with controlled average diameters of 27.5 nm from ambient carbon dioxide captured and dissolved in molten carbonate electrolytes. ALD of passive alumina coatings on a Ni anode prevents electrode corrosion processes and adverse deposition of Ni on the cathode that results in increased CNT diameters, lower CNT quality, and non-CNT products. On the cathode side where CNT growth occurs, our results elucidate the fine balance of iron catalyst accessibility from the cathode interior and the surface chemical properties in order to achieve high yield and high quality CNT growth. Our work provides an intersection between decades of research understanding on catalytic gas-phase growth of CNT materials and the ability to leverage these ideas to sustainably capture ambient carbon dioxide and produce functional CNT materials.

Growth of MWCNTs on Flexible Stainless Steels without Additional Catalysts

Multiwalled carbon nanotubes (MWCNTs) were synthesized on austenitic stainless steel foils (Type 304) using a home-built thermal chemical vapor deposition (CVD) under atmospheric pressure of hydrogen (H2) and acetylene (C2H2). During the growth, the stainless steel substrates were heated at different temperatures of 600, 700, 800, and 900°C. It was found that MWCNTs were grown on the stainless steel substrates heated at 600, 700, and 800°C while amorphous carbon film was grown at 900°C. The diameters of MWCNTs, as identified by scanning electron microscope (SEM) images together with ImageJ software program, were found to be 67.7, 43.0, and 33.1 nm, respectively. The crystallinity of MWCNTs was investigated by an X-ray diffractometer. The number of graphitic walled layers and the inner diameter of MWCNTs were investigated using a transmission electron microscope (TEM). The occurrence of Fe3O4 nanoparticles associated with carbon element can be used to reveal the behavior of Fe in stainless steel as catalyst. Raman spectroscopy was used to confirm the growth and quality of MWCNTs. The results obtained in this work showed that the optimum heated stainless steel substrate temperature for the growth of effective MWCNTs is 700°C. Chemical states of MWCNTs were investigated by X-ray photoelectron spectroscopy (XPS) using synchrotron light.

Buffer Film Assisted Growth of Dense MWCNTs on Copper Foils for Flexible Electrochemical Applications

The novel Inconel buffer films were prepared on copper foils using unbalance direct current (DC) magnetron sputtering. These films were employed as buffer layers for supporting the dense growth of multiwalled carbon nanotubes (MWCNTs). Thermal chemical vapor deposition (CVD) with metal alloys such as stainless steel (SS) type 304 films was considered to synthesize MWCNTs. To understand the effectiveness of these buffer films, the MWCNTs grown on buffer-free layer were carried out as a comparison. The main problem such as the diffusion of catalysts into the oxide layer of metal substrate during the CVD process was solved together with a creation of good electrical contact between substrate and nanotubes. The morphologies, crystallinities, and electrochemical behaviors of MWCNTs grown on Inconel buffer films with 304 SS catalysts revealed the better results for applying in flexible electrochemical applications.

Verification of Mechanism for the Formation of Carbon Nanotetrahedra Using Electron Beam Tomography.

When a carbon nanotube is flattened in two different directions, a nanotetrahedron is formed between the two nanoribbons. The distribution of the angles between the nanoribbons provides a clue to understanding the mechanism for the formation of nanotetrahedra. In this study, the angles between nanoribbons are measured using transmission electron microscopy-based electron beam tomography. The results are consistent with the proposed origami mechanism, in which the direction of flattening changes by approximately 90° during the growth of multi-walled carbon nanotubes.

Effect of Gas Flowrate on Nucleation Mechanism of MWCNTs for a Compound Catalyst

Activation of the catalyst particles during a CVD process can be anticipated from the carbon feeding rate. In this study, Fe2O3/Al2O3 catalyst was synthesized with uniformly dispersed iron over alumina support for onward production of multiwalled carbon nanotubes (MWCNTs) in a fluidized bed chemical CVD reactor. The effect of the ethylene flowrate on catalytic activity of the compound catalyst and morphology of the as-grown MWCNTs was also investigated in this study. The dispersed active phases of the catalyst and optimized gas flowrate helped in improving the tube morphology and prevented the aggregation of the as-grown MWCNTs. The flowrates, below 100 sccm, did not provide sufficient reactants to interact with the catalyst for production of defect-free CNT structures. Above 100 sccm, concentration of the carbon precursor did not show notable influence on decomposition rate of the gas molecules. The most promising results on growth and structural properties of MWCNTs were gained at ethylene flowrate of 100 sccm. At this flowrate, the ratio of G and D intensity peaks (IG/ID) was deliberated about 1.40, which indicates the growth of graphitic structures of MWCNTs.

Impact of Multi-Walled Carbon Nanotube Fabrication on Carbon Cloth Electrodes for Hydrogen-Vanadium Reversible Fuel Cells

The surface area of carbon electrodes in redox flow batteries and fuel cells governs the rates of electrochemical reactions. Carbon cloth electrodes offer greater durability and serve as a potential substitute for conventional carbon paper electrodes. Growing multi-walled carbon nanotubes (MWCNTs) on carbon cloth electrodes is an effective way to increase the surface area and overall performance of these devices. In this study, electrodeposited cobalt nanoparticles were used as seed catalysts to synthesize MWCNTs onto carbon cloth through chemical vapor deposition. Scanning electron microscopy and energy dispersive X-ray analysis confirmed cobalt deposition and uniform MWCNT growth throughout the carbon cloth electrode. The MWCNT cloth, MWCNT paper, and plain carbon cloth were tested in a 3-electrode electrochemical arrangement and a hydrogen-vanadium reversible fuel cell to determine surface enhancement factors and fuel cell performances, respectively. The MWCNT cloth and MWCNT paper have 2–3 times the surface area of their respective conventional substrates. The hydrogen-vanadium reversible fuel cell with MWCNT carbon cloth electrode has a peak power performance of 0.61 W mg−1 cm−2, compared to 0.54 W mg−1 cm−2 for MWCNT carbon paper and 0.29 W mg−1 cm−2 for plain carbon cloth.

Effective aqueous arsenic removal using zero valent iron doped MWCNT synthesized by in situ CVD method using natural α-Fe2O3 as a precursor

This research presents an efficient system for removing aqua's arsenic based on in situ zero valent iron doping onto multiwall carbon nanotube (MWCNT) through MWCNT growth onto the natural α-Fe2O3 surface in chemical vapor deposition (CVD) reactor. The as-synthesized magnetic nanohybrid was characterized by XRD, VSM, FE–SEM and TEM techniques. The result of XRD analysis revealed that MWCNT has been successfully generated on the surface of zero valent iron. Moreover, the material showed good superparamagnetic characteristic to be employed as a magnetic adsorbent. The hematite, nanohybrid and its air oxidized form were used for removing aqueous arsenite and arsenate; however, non oxidized material exhibited greater efficiency for the analytes uptake. Equilibrium times were 60 and 90 min for arsenate and arsenite adsorption using nanohybrid and oxidized sorbent but the equilibrium time was 1320 min using hematite. The adsorption efficiencies of hematite and oxidized sorbent were 18, 74% and 26, 77% for arsenite and arsenate, respectively, at initial concentration of 10 mg L−1. At this situation, the removal efficiencies were 96 and 98.5% for arsenite and arsenate adsorption using raw nanohybrid. Thermodynamic study was also performed and results indicated that arsenic adsorption onto nanohybrid and oxidized sorbent was spontaneous however hematite followed a nonspontaneous path for the arsenic removal.

Ni-Co bimetal nanowires filled multiwalled carbon nanotubes for the highly sensitive and selective non-enzymatic glucose sensor applications.

The facile, time and cost efficient and environmental benign approach has been developed for the preparation of Nickel (Ni)-Cobalt (Co) alloy nanowires filled multiwalled carbon nanotubes (MWCNTs) with the aid of mesoporous silica nanoparticles (MSN)/Ni-Co catalyst. The controlled incorporation of Ni-Co nanostructures in the three dimensional (3D) pore structures of MSN yielded the catalytically active system for the MWCNT growth. The inner surface of MWCNTs was quasi-continuously filled with face-centered cubic (fcc) structured Ni-Co nanowires. The as-prepared nanostructures were exploited as non-enzymatic electrochemical sensor probes for the reliable detection of glucose. The electrochemical measurements illustrated that the fabricated sensor exhibited an excellent electrochemical performance toward glucose oxidation with a high sensitivity of 0.695 mA mM−1 cm−2, low detection limit of 1.2 μM, a wide linear range from 5 μM–10 mM and good selectivity. The unprecedented electrochemical performances obtained for the prepared nanocomposite are purely attributed to the synergistic effects of Ni-Co nanowires and MWCNTs. The constructed facile, selective and sensitive glucose sensor has also endowed its reliability in analyzing the human serum samples, which wide opened the new findings for exploring the novel nanostructures based glucose sensor devices with affordable cost and good stability.

Radial growth of multi-walled carbon nanotubes in aligned sheets through cyclic carbon deposition and graphitization

Carbon coated aligned multi-walled carbon nanotube (AMWCNT/C) sheets were used for studying the controlled radial growth of MWCNTs. Pyrolytic carbon (PyC) was deposited on the surface of nanotubes using multiple cycles of chemical vapor infiltration. Morphological and structural characterization showed that when graphitization was done in one step, after the deposition of multiple cycles of PyC, the presence of a large amount of disordered carbon on the surface of nanotubes led to a poorly graphitized coating structure that did not resembled nanotube walls anymore. Graphitization of the AMWCNT/C sheets after each deposition cycle prevented the development of disordered carbon during the subsequent PyC deposition cycles. Using the cyclic-graphitization method, thick PyC coating layers were successfully graphitized into a crystalline structure that could not be differentiated from the original nanotube walls. TEM observation and X-ray data confirmed radial growth of nanotubes, while spectra collected from Raman spectroscopy revealed that radially grown CNTs had the same quality as graphitized pristine nanotubes. The focus of this study was to compare the effect of cyclic graphitization with a one-step graphitization method to gain insight on the necessary parameters needed to radially grow high quality CNTs.

CVD Grown Mwcnts and Graphene for Pemfcs Application

In this paper we report the development of Multi-Walled Carbon Nanotubes (MWCNTs) and graphene via chemical vapor deposition (CVD) for PEM Fuel Cells applications. MWCNTs growth are achieved by the flow of ethylene and hydrogen gasses over iron beased catalytic substrates at different temperatures and gas flow. Graphene growth is carried out by the flow of methane and hydrogen gasses over various thickness cupper substrates cleaned by different methods (electropolishing, acetone and acetic acid) at low (500 mTorr) and atmospheric pressure. Characterization is performed with XRD, optical microscopy (SEM/EDS) and Raman/AFM spectroscopy. Results show noticeable differences in Raman signals and optical color contrast regarding the preferential growth of MWCNTs, and between the number and quality of layers of graphene and graphite, as well as distinctions between single-to-few- and multi-layer graphene, respectively. The electrochemical behavior of CVD grown MWCNTs and graphene are studied by cycling voltammetry on rotating disk electrode (RDE) to determine the activity of toward oxygen reduction reaction (ORR). Scanning Electrochemical Microscopy (SECM) is used to shows the localized electrochemical behavior difference between the MWCNTs and graphenes.

Photocurrent generation in carbon nanotube/cubic-phase HfO2 nanoparticle hybrid nanocomposites.

A hybrid material consisting of nonfunctionalized multiwall carbon nanotubes (MWCNTs) and cubic-phase HfO2 nanoparticles (NPs) with an average diameter of 2.6 nm has been synthesized. Free standing HfO2 NPs present unusual optical properties and a strong photoluminescence emission in the visible region, originating from surface defects. Transmission electron microscopy studies show that these NPs decorate the MWCNTs on topological defect sites. The electronic structure of the C K-edge in the nanocomposites was probed by electron energy loss spectroscopy, highlighting the key role of the MWCNT growth defects in anchoring HfO2 NPs. A combined optical emission and absorption spectroscopy approach illustrated that, in contrast to HfO2 NPs, the metallic MWCNTs do not emit light but instead expose their discrete electronic structure in the absorption spectra. The hybrid material manifests characteristic absorption features with a gradual merger of the MWCNT π-plasmon resonance band with the intrinsic defect band and fundamental edge of HfO2. The photoluminescence of the nanocomposites indicates features attributed to combined effects of charge desaturation of HfO2 surface states and charge transfer to the MWCNTs with an overall reduction of radiative recombination. Finally, photocurrent generation under UV–vis illumination suggests that a HfO2 NP/MWCNT hybrid system can be used as a flexible nanodevice for light harvesting applications.

Effect of Ferrocene Catalyst and Hydrogen Feed on Microstructures of Vertically Aligned MWCNTs

This study investigated the effect of catalyst amount on chemical vapour deposition (CVD) growth of multi-walled carbon nanotubes (MWCNTs) with and without hydrogen feed. The ferrocene weight was varied from 100 mg to 200 mg for CNTs growth over Si/SiO2/Al2O3 substrate. Very few CNTs were seen in micrographs of the samples produced in the absence of the hydrogen feed. Most of the carbon atoms precipitated into amorphous carbon due to existence of inactive catalyst particles. However, CNT structures grown with hydrogen feed were more distinct; the nanotubes were thinner, straight and highly crystalline. MWCNTs arrays/forest length was also increased from 120 µm to 850 µm with hydrogen feed. An increase in catalyst weight significantly affected the diameter, crystallinity, alignment and growth of nanotubes. The lowest inner-shell spacing of 0.348 nm was obtained with 150 mg of ferrocene, which is an indication of growth of relatively pure CNTs. Under the optimum conditions, the areal density of the ferrocene particles was sufficiently increased to get required alignment and crystallinity of MWCNTs.

Effect of Interwall Interaction on Phonon Oscillations of Growing Multi-Walled Carbon Nanotube

In this paper, a novel model is presented to explain the growth mechanism of multi-walled carbon nanotube (MWCNT) in chemical vapor deposition. The developed model is based on kinetic theory of gases and interlayer interaction between neighbor walls of MWCNT in addition to phonon vibrations of MWCNT on substrate. All interactions including MWCNT-catalyst and interlayer are investigated by Lennard-Jones potential. Simulations demonstrate that the growth of walls of MWCNT is saturated at a certain time. In addition, effect of temperature and type of catalyst on growth is investigated and it is shown that there is an optimum temperature and an optimum catalyst for growth process. Also it is shown that the optimum temperature is changed using different catalysts. Finally, effect of the partial pressure of decomposed hydrocarbons on the MWCNT growth is presented. It is shown that increasing partial pressure leads to longest MWCNTs and influence of partial pressure on MWCNTs with smaller diameter of outer wall is stronger. All results are in good agreement with reported experimental results, so it can be useful in future experimental and theoretical researches for optimization of MWCNT growth.

Catalytic Chemical Vapour Deposition on MFe<SUB>2</SUB>O<SUB>4</SUB>–SiO<SUB>2</SUB> (M = Co, Mn, Ni) Nanocomposite Aerogel Catalysts for the Production of Multi Walled Carbon Nanotubes

Highly porous MFe2O4-SiO2 (M = Co, Mn, Ni) nanocomposite aerogels were tested for the first time as catalysts for multi walled carbon nanotubes production by Catalytic Chemical Vapour Deposition. Structural and textural characterization points out that the catalysts are made out of nanocomposites where nanocrystalline ferrite phases with controlled composition and size in the range 9-13 nm are finely dispersed into the highly porous silica support. Remarkably, CoFe2O4-SiO2 and MnFe2O4-SiO2 catalysts have shown poor catalytic activity, whereas NiFe2O4-SiO2 catalyst has given rise to good quality nanotubes with high yields at deposition temperatures in the range 500-650 °C. The different catalytic behaviour of the mixed ferrite-silica aerogels as a function of the bivalent metal (M = Co, Mn, Ni) can been ascribed to how easily the nanophase can be reduced. In particular, it was demonstrated that the most active NiFe2O4 nanoparticles undergo an in-situ reduction process during the Catalytic Chemical Vapour Deposition reaction, forming a NiFe alloy phase that is responsible for promoting the multi walled carbon nanotubes growth.

Linear carbon chains inside multi-walled carbon nanotubes: Growth mechanism, thermal stability and electrical properties

Linear carbon chains (LCCs) consisting of sp-hybridized carbon atoms are considered a fascinating 1D system and could be used in the fabrication of the next-generation molecular devices because of its ideal linear atomic nature. A large portion of long LCCs inside multi-walled carbon nanotubes (MWCNTs) were synthesized by atmospheric arc discharge in the presence of boron. Closed-end growth of MWCNTs in the arc process is suggested as a critical condition for the simultaneous growth of LCCs within the inner cores of carbon nanotubes. The strong Raman line around 1850 cm−1 was used to characterize the degree of filling as well as their structural stability under high temperature thermal treatments. We observed a distinctive change in the electrical conductivity of the MWCNT assembly before and after the disappearance of LCCs due to the expected strong coupling interaction between the LCCs and the innermost tube. This work demonstrates for the first time the enhanced effect of confined linear carbon chains on the overall electrical conductivity of MWCNT assemblies.

Catalytic action of graphene oxide towards the growth of carbon nanotubes

We have studied the growth of multiwall carbon nanotubes (CNTs), using graphene oxide (GO) and iron nanoparticles as catalyst for chemical vapor deposition (CVD) technique. This approach is based on covalent bonding between GO and acetylene (C2H2) gas molecules. Catalytic layers of GO and iron nanoparticles were fabricated on copper substrate using spin coater. Main reactions took place in CVD chamber under atmospheric pressure at 750°C. Field emission scanning electron microscope (FESEM) explored the diameter distribution of successfully synthesized CNTs: 10–20nm for GO and 29–47nm for iron nanoparticles. X-ray diffraction spectra confirmed the presence of synthesized CNTs on both catalysts, as well as transformation of GO to reduced graphene oxide (rGO) during this process. ID/IG ratio was obtained through Raman spectroscopy, which revealed less defect contents in CNTs synthesized on GO in comparison to nanotubes grown iron catalyst. The main advantages of this innovative approach are simplicity, low cost due to one step technique, high yield and less defects.

Study of surface defects and crystallinity of MWCNTs growth in FCCVD

Abstract This research investigated the structural growth of multiwalled carbon nanotubes (MWCNTs) in a double stage horizontal chemical vapor deposition (CVD) reactor. Ethylene was used as a carbon source for nucleation of nanotubes. Ferrocene catalyst weight was varied from 0.1 to 0.2 g to demonstrate the growth of MWCNTs on Si/SiO2/Al2O3 substrate. The obtained data revealed that the weight of the catalyst significantly affects the diameter, crystallinity, alignment and yield of the nanotubes. Lower inner-shell spacing and the ratio of D-Raman peak intensity and G-Raman peak intensity (ID/IG ratio) were obtained with 0.15 g of ferrocene, which was an indication of relatively pure carbon nanotubes (CNTs) growth. Raman spectra also confirmed the highly crystalline and relatively pure CNTs structures with ID/IG ratio of 0.700. TGA data revealed the formation of 97% pure nanotubes with oxidation temperature of 620°C. However, above and below the optimum (0.15 g of ferrocene), some of the grown CNTs were found defective and few black spots were also seen in TEM micrographs.

The Effect of Catalyst Composition on the Growth of Multi-Walled Carbon Nanotubes from Methyl Esters of Oryza sativa Oil

The Effect of Catalyst Composition on the Growth of Multi-Walled Carbon Nanotubes from Methyl Esters of Oryza sativa Oil

Effect of Varying Inert Gas and Acetylene Concentration on the Synthesis of Carbon Nanotubes

The multiwalled carbon nanotubes (MWCNTs) with small diameter and high purity were achieved by chemical vapor deposition technique using silicon substrate. The introduction of specific concentration of inert gas with hydrocarbon played a key role in controlling morphology and diameter of MWCNTs. Nickel mixed ferrite nanoparticles were used as a catalyst for the growth of MWCNTs. Growth parameters like concentration of hydrocarbon source and inert gas flow, composition of catalyst particles and growth temperature were studied. In this work smaller diameter and twisted MWCNTs were formed by dilution of acetylene with argon gas. Electrical properties suggest a semimetallic behavior of synthesized MWCNTs.

A novel combination of simple foaming and freeze-drying processes for making carbon foam containing multiwalled carbon nanotubes

To fabricate carbon foam with high surface area and electrical conductivity, a novel combination of foaming followed by growth of multi-walled carbon nanotubes (MWCNTs) aerogel inside the porous body has been investigated. Open cell sucrose based carbon foam was prepared by thermo-foaming and dehydration at 250°C. A well-dispersed 1.5wt% MWCNTs aqueous solution in carboxyl methyl cellulose was vacuum impregnated into the porous body and lyophilized using a freeze-drying process. The resulting macro to mesoporous morphology was characterized by scanning electron microscopy and nitrogen porosimetry. Due to the lower thermal conductivity of hydrated carbon foam, the MWCNTs/carbon foam exhibited a random cellular-type morphology with crinkly and curvy sheets of nanotubes. The prepared MWCNTs/carbon foam displayed a very low density of 0.24gcm−3 and a fairly high compressive strength of 1.45MPa. The electrical conductivity being 0.021Scm−1, improved eight orders of magnitude compared to that of the dehydrated carbon foam without MWCNTs. Surface area as high as 320m2g−1 with the pore size distribution centered at 25 and 150nm and macro to meso porous morphology was achieved which can be considered for various energy storage and environmental applications.